In the field of high voltage electronic devices, it is known to implement high voltage (e.g. ˜1500V) isolation between a low voltage (e.g. ˜5V) control integrated circuit (IC) device and a high voltage output driver module. Such isolation is required in order to avoid shorting between the high voltage output and the low voltage control circuitry.
Typically, such high voltage isolation is implemented using galvanic isolation. Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no metallic conduction path is permitted. Energy or information can still be exchanged between the sections by other means, such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical means.
In some applications it is desirable to implement a dual slew rate for a high voltage output driver. For example, a first (fast) turn off rate of, say, an insulated-gate bipolar transistor (IGBT) device may be required to be implemented in order to optimise the turn off energy of the IGBT device. In addition, a second (slow) turn off rate of the IGBT device may be required to be implemented in order to avoid overshoot of a load current.
Implementation of such a dual slew rate requires two kinds of information to be conveyed from the control component to the high voltage output driver module: 1) information for controlling the turning on and off of the driver device; and 2) information for controlling the slew rate (i.e. controlling whether the driver device is turned off at a fast rate or a slow rate). A conventional approach for conveying the two kinds of information from the control component to the high voltage output driver module is to use two coupling channels: a first signal for controlling the turning on and off of the driver device; a second signal controlling the slew rate. An example of such a conventional approach is illustrated and described in U.S. Pat. No. 7,741,896.
A problem with this conventional approach is that in order to maintain the isolation between the low voltage control circuitry and the high voltage driver module, isolation circuits have to be implemented for both of the two coupling channels. Such isolation circuits require a significant amount of die area, and thus the need for duplication of the isolation circuits is undesirable.